The prior art discloses a variety of methods and apparatus which produce solid material directly from a source of molten material. Most prior art systems are for the fabrication of metal products and use some type of fixed, rigid, noncontrollable forming orifice to stabilize the dimensions of the product.
A typical system of this type is illustrated in U.S. Pat. No 2,825,108, which discloses molten metal being made into filamentary form by forcing it through an orifice so as to generate a free standing stream of molten material which is subsequently solidified into filamentary form on a rotating, heat-extracting member. The rate of production is determined by the rate at which the molten material is expelled from the orifice and for continuous filament this rate must be approximately synchronous with the rate of movement of the heat extracting member at its point of contact with the filament.
U.S. Pat. No. 3,838,185 to Maringer et al. discloses a disc-like heat extracting substrate which is rotated and lowered into the upper surface of a molten material. The peripheral edge of the disc-like substrate is generally parallel to the surface of the molten material. More specifically, the edge moves slightly downwardly through the surface of the melt into a region of contact and then moves upwardly and out of the melt carrying a layer of molten material which is then chilled as the wheel rotates and carries it away from the surface of the molten material. After the layer is solidified, it is removed from the substrate in the form of a filamentary product without the use of forming orifices.
One difficulty with this system however, is that, because the heat extracting substrate is inserted downwardly into the surface of the melt, the melt surface must be open and exposed to the atmosphere. This exposure to the atmosphere is a major source of heat loss and therefore increases the energy required to maintain the molten material surface at a suitably high temperature for proper operation of the system. Secondly, the position of the heat extracting substrate over the melt does not allow line of sight access to the melt, which is necessary for efficient melting with a directed energy source like a plasma, an electron beam or a laser. The heat extracting substrate casts a shadow over the melt that may result in either a semi-solid or frozen melt pool and thus inhibits casting of filament. Further, this system permits limited control because the region of contact of the melt with the substrate must always be at the lower-most segment of the substrate. Thus, control of the process is limited to control of the substrate speed, depth of penetration of a substrate into the surface of the molten material and the temperature.
The second system for overcoming some of these objectional characteristics is disclosed in U.S. Pat. No. 3,896,203 to Maringer et al. In this patent, a melted drop of material is adhered to a solid member by means of the molecular attraction of the molten material of the solid member to form an adherent pendant drop. The drop is suspended from the solid member. The drop remains adherent because the net molecular attraction force is greater than the net gravitational force on the drop. The adherent pendant drop is then contacted by a rotating, heat-extracting member. The pendant drop may be formed by locally heating the end of the solid member of the material to melt the end. Alternatively, the pendant may be formed, adhered to and suspended from a orifice through which melt is forced, for example, by the pressure head exerted by the height of molten material above the orifice. However, this system has also been hampered by a variety of difficulties, particularly in connection with the instability of the pendant drop mechanism.
U.S. Pat. No. 993,904 to Strange discloses a primitive version of which is the preferred process in which to utilize the apparatus of the present invention.
The art of molten metal casting onto substrates has extremely limited experience in developing a tiltable crucible in connection with the formation of molten material products. U.S. Pat. No. 4,582,116 to Ray et al. discloses a system utilizing a tiltable cooled crucible which contains molten alloy and has a spout for extracting the molten alloy. The alloy is then cast into film products on an advancing chilled surface. The disadvantage of this process is that the axis of rotation of the crucible is along the interface between the crucible and chill block. As the crucible tilts, the gap between it and the moving chill surface varies, depending on the depth of the pouring spout on the crucible. This varying distance between the pour spout and moving chill surface is most undesirable and leads to variations in the thickness of the film deposited on the chill surface.
U.S. Pat. No. 4,612,973 to Whang discloses a cold hearth melt spinning apparatus for continuous casting of refractory and reactive alloys. The apparatus utilizes a cold crucible which has a selectively grooved surface operative to reduce both melt freezing at the melt/crucible interface and input heating power requirements and a replaceable nozzle of a refractory material that is friction fit into an aperture provided therefore in the crucible. The disadvantage of this apparatus is that the reactive liquid must be extruded through a nozzle, thus leading to chemical contamination of the liquid or blocking of the nozzle by freezing of the liquid in the orifice.
U.S. Pat. No. 4,471,831 discloses an apparatus for rapid solidification casting of molten, high-temperature and/or reactive metallic alloys, which has a heat extraction crucible for containing the alloy in liquid form. A nozzle forms an integral part of the crucible and allows for ejection of a stream of molten metal. The heat extracting crucible and nozzle are protected from a molten alloy by a shell of the alloy which has solidified and prevents reaction between the molten metal and the heat extracting crucible. The disadvantage of this apparatus is that the flow through the nozzle cannot be controlled by the apparatus to ensure that the reservoir of liquid is chemically homogeneous before pouring, or that the cooled nozzle will not freeze the liquid and block the flow through the nozzle.
U.S. Pat. No. 4,705,095 describes an improved heat extracting chill block roll and an accompanying method for use in the continuous casting of ribbon-like metal sheet directly from the melt by means of rapid solidification techniques. The resulting product is thicker and more uniform than previously possible utilizing prior art methods and apparatus.
Accordingly, it is an object of the invention to provide an improved apparatus system for forming ribbon, filament, fiber, or film products directly from a molten material that is particularly suitable for positioning and maintaining a constant relationship between the position of the crucible edge over which the molten metal overflows onto a substrate. Without such a system major problems, i.e., material spillage, can arise which result from the small distance separating the receptacle and the chilling substrate.
Other objects and features of the invention are described below and will become apparent from the following detailed description.